1. Field of the Invention
The present invention relates to data security in a wireless network system, and more particularly, to an apparatus and method for data security in a wireless network system, which protect data by encrypting data frames to be transmitted, including their Medium Access Control (MAC) header and payload, with an Initialization Vector (IV) modified at each set state in the wireless network system.
2. Description of the Related Art
In general, stations, such as Personal Computers (PCs), Personal Digital Assistants (PDAs), notebook computers and the like, connect to a Local Area Network (LAN) and share several types of data or information with one another.
LAN systems can be classified into a wired LAN system and a Wireless LAN (WLAN) system depending on whether the movement of stations is allowed.
The wired LAN systems connect to one another and share information and resources via the cable at their fixed position. The use of the cable makes it inconvenient for users to move and requires a technical cabling task in moving the wired LAN systems. Furthermore, the maintenance of wired LAN systems consumes much time, obstructing tasks.
In the WLAN system, a communication between stations is performed via a wireless medium using a radio frequency or light. The WLAN systems have been developed with the advent of recent advanced Internet services and wireless communications technologies. The use of the WLAN system has proliferated because it is capable of being constructed for network connections between buildings and at places such as large-scale offices or physical-distribution centers where a wired network is difficult to construct, and provides facilitated maintenance.
The WLAN system is composed of Access Points (APs) and stations. The AP sends radio frequencies to enable WLAN users within its coverage area to unitize Internet connections and networks, and acts as a base station of cellular telephones or a hub of a wired network. For high-speed wireless Internet services provided by Internet Service Providers (ISPs), APs are disposed within a service area.
Stations are required to have a WLAN card to perform wireless network communications. Stations can be Personal Computers (PCs including notebook computers) and PDAs.
Recently, a WLAN standard, widely used, is IEEE 802.11 that conforms to “Standard for Information technology-Telecommunications and information exchange between systems-Local and metropolitan area networks-Specific requirements-Parts? Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications” 1999 Edition.
In the IEEE 802.11 standard, a basic construction block for a network is a Basic Service Set (BSS). An IEEE 802.11 network includes an independent BSS in which stations in BSS perform direct communication there between, an infrastructure BSS in which a station in BSS communicates with a station inside or outside the BSS via an AP, and an extended service set that extends a service area through a connection between BSS and BSS.
The WLAN system has several shortcomings associated with security because of its characteristics of using radio frequencies for communications.
First, unauthorized users are allowed to easily access network resources. A physical approach to a network is necessary to access a wired LAN system and utilize network resources. For example, to utilize a wired LAN system, one has to enter an office or a building where the wired LAN system is constructed, making it difficult for unauthorized users to utilize network resources. However, in WLAN systems, accessing the network resources requires only that radio frequencies emitted from a user's station arrives at an AP. The radio frequencies penetrate walls, ceilings, and bottoms and thus unauthorized users are actually allowed to employ network resources without being discovered. Consequently, this introduces an authentication mechanism into the WLAN system so that only authorized users employ network resources.
In a wired LAN system environment, data transmitted from a sending station to a receiving station is less discovered by unauthorized users because the data is conveyed over a determined medium. In a WLAN system environment, data is conveyed on radio frequencies and thus there is a risk that the data is exposed to unauthorized users in places at which the radio frequencies arrive. Accordingly, there is a need, in the WLAN system environment, for a mechanism that encrypts data so as not to be exposed to unauthorized users.
To provide security for a WLAN system, access control and data confidentiality are supported. The access control is performed through user authentication by the following methods: a method in which authorized users and an AP have the same share key that is used for authentication upon an access request, a method in which a MAC address of a WLAN card mounted on an authorized user's station is directly input to the AP, and an IEEE 802.11x authentication method in which users perform an authentication procedure with respect to an authentication server by use of his or her authentication information.
Data confidentiality is supported using a Wired Equivalent Privacy (WEP) algorithm in which a key length used is 40 or 104 bits.
Furthermore, the IEEE 802.11i standard prescribes IEEE 802.1x/1aa based access control, security session management, dynamic key exchange and management, and a new symmetric key encryption algorithm applied to provide data protection in wireless sections in order to address shortcomings of an IEEE 802.11 WLAN system associated with security in the wireless sections. In other words, the IEEE 802.11x/1aa standard prescribes a framework of user authentication and key exchange while the IEEE 802.11i standard prescribes the use of IEEE 802.1x/1aa as a great framework of the user authentication and the key exchange. Moreover, the IEEE 802.11i defines a 4-way handshake scheme as a key exchange scheme, a hierarchy of an exchanged key, and cipher suites for new wireless sections.
In the security algorithm, keys are used to encrypt/decrypt data. The keys for data encryption/decryption are imparted using a Pre-Shared Key (PSK) scheme and through an authentication server, as prescribed in the IEEE 802.1x standard.
There are two types of keys that are imparted to stations and APs: a pair-wise key intended to distinguish between the stations and the APs and a group key that is broadcast to be shared between the APs and the stations within the service area of the APs.
The thus imparted keys or a combination of the keys and an IV are used to encrypt or decrypt data between a station and an AP or between a station and a station. The use of an IV allows dynamic data encryption.
The encryption with the key shared between the station and the AP and between the station and the station or with a combination of the shared key and an IV is performed only on a payload of a frame as a data transfer unit and not an MAC header portion, which contains information about the stations and the network. In other words, an IV, which is contained in the MAC header portion of the frame used to transfer data, is not encrypted but transferred in the form of a plain text. This exposes any information contained in an IV to stations within the service area of the AP, increasing a risk of information hacking.
To address this problem, encryption has been attempted even below a data link layer. In other words, efforts have been done to increase frame invisibility by encrypting even the MAC header of the frame. This will be referred to as physical layer encryption. However, the physical layer encryption uses only a fixed key sequence instead of an IV. If any stations located within the service area of the AP are aware of the fixed key sequence, transmitted frames would be exposed to hacking, degrading the effectiveness of security.